1. Field of the Invention
The present invention relates generally to a spindle motor and, more particularly, to a spindle motor which is capable of more easily controlling an axial gap and levelness between the thrust plate of a rotating shaft and a sealing cap.
2. Description of the Related Art
Generally, a spindle motor maintains the rotational characteristics of high precision, because a bearing housing a rotating shaft therein rotatably supports the rotating shaft. Because of these characteristics, the spindle motor has been widely used as the drive means of hard-disk drives, optical disk drives, magnetic disk drives and other recording media requiring high-speed rotation.
In such a spindle motor, a hydrodynamic bearing is generally used to inject a predetermined fluid between a rotating shaft and a sleeve for the axial support of the rotating shaft so that the rotating shaft may easily rotate, and to generate dynamic pressure when the rotating shaft rotates.
The hydrodynamic bearing may have a dynamic pressure-generating groove so as to generate dynamic pressure of the fluid during the rotation of the rotating shaft. Such a dynamic pressure-generating groove may be formed in each of the inner circumferential part of the sleeve which rotatably supports the rotating shaft and a thrust plate which is installed perpendicular to the axial direction of the rotating shaft. One example of the conventional spindle motor is illustrated in FIG. 6.
As shown in FIG. 6, the conventional spindle motor includes a plate 10, a sleeve 20, an armature 30, a rotating shaft 40, a thrust plate 50, a hub 60 and a sealing cap 70.
The plate 10 is mounted to a device such as a hard-disk drive, and the sleeve 20 is secured to the central portion of the plate 10 through press-fitting.
The sleeve 20 rotatably accommodates the rotating shaft 40 therein, and the sealing cap 70 is secured to the upper portion of the sleeve so as to prevent the removal of the thrust plate 50 and the rotating shaft 40. Further, the sleeve 20 has hydrodynamic bearings on the inner circumference facing the rotating shaft 40 and a portion facing the thrust plate 50.
When external power is applied to the armature 30, the armature 30 forms an electric field so as to rotate the hub 60 on which an optical or magnetic disk is mounted. The armature 30 includes a core 31 which is formed by laminating a plurality of metal sheets and a coil 32 which is wound several times on the core 31.
The rotating shaft 40 axially supports the hub 60, and is inserted into the sleeve 20 to be rotatably supported by the sleeve 20. The thrust plate 50 is secured to the upper portion of the rotating shaft 40.
The thrust plate 50 is secured to the rotating shaft 40. An upper thrust bearing is provided between the thrust plate 50 and the sealing cap 70, and a lower thrust bearing is provided between the thrust plate 50 and the sleeve 20. Here, the lower thrust bearing generates fluid dynamic pressure using a fluid stored between the sleeve 20 and the thrust plate 50 during the rotation of the rotating shaft 40, thus floating the thrust plate 50 from the sleeve 20. That is, owing to the lower thrust hydrodynamic bearing, the thrust plate 50 is not in contact with the sleeve 20 during the rotation of the rotating shaft 40. Further, the upper thrust bearing generates fluid dynamic pressure using fluid between the thrust plate 50 and the sealing cap 70 during the rotation of the rotating shaft 40, so that the non-contact state between the thrust plate 50 and the sealing cap 70 is maintained.
The hub 60 mounts the optical or magnetic disk (not shown) thereon to rotate it. A magnet 61 which forms a magnetic force is secured to the inner circumference of the hub 60 in such a way as to face the armature 30.
The sealing cap 70 is secured to the sleeve 20 in such a way as to face the thrust plate 50. A fluid sealing part 71 is formed between the sealing cap 70 and the thrust plate 50 to store fluid. Further, a gap must be maintained between the sealing cap 70 and the thrust plate 50 to form the upper thrust bearing.
Meanwhile, in the conventional spindle motor having the above construction, the sealing cap 70 is welded to the sleeve 20 through laser welding or the like and a predetermined gap is maintained between the sealing cap 70 and the thrust plate 50. However, during the laser welding process for the coupling of the sealing cap 70, the sealing cap 70 may become deformed or curved due to the hardening of a weld part 80 and the residual stress applied to the sealing cap 70.
In detail, as shown in FIGS. 7 and 8, in the case where the sealing cap 70 is seated on the sleeve 20 and thereafter a junction between the sealing cap 70 and the sleeve 20 is welded using a laser welding machine or the like, as shown in FIG. 8, the inner circumference of the sealing cap 70 may be bent upwards (the direction shown by the arrow) or damaged.
That is, during the laser welding of the sealing cap 70, the gap and the levelness between the sealing cap 70 and the thrust plate 50 cannot be kept constant. Hence, it is difficult to obtain the stable drive characteristics of the spindle motor.